/Engine/Source/Runtime/RHI/Public/RHICommandList.h
EBufferUsageFlags::MultiGPUAllocate is only needed for cases where CPU initialized data needs to be different per GPU, which is a rare edge case. Currently, this is only used for the ray tracing acceleration structure address buffer, which contains virtual address references to other GPU resources, which may be in a different location on each GPU.
void * LockBufferMGPU ( [FRHIBuffer](API\Runtime\RHI\FRHIBuffer) * Buffer, uint32 GPUIndex, uint32 Offset, uint32 SizeRHI, EResourceLockMode LockMode )